I don't know why people are blaming "political correctness". This is nothing to do with political correctness. Political correctness is the modern term for what used to be called politeness, trying to avoid offensive terms, amending things like language so as not to ostracise/ demonise/ "other". Political correctness is about no longer using that phrase that was apparently acceptable in the 1970s, it's about trying to avoid stereotypes or derogatory language.
This, however, is about accessibility, which is about equality. And equality, as the law stands right now, means trying to accommodate people's needs where possible (maybe that can be accommodated by guaranteeing a taxi for people unable to board a train, but it doesn't mean ignoring people's needs).
I don't know why "political correctness" has become the phrase for anything that people don't like (?) but it's not the phrase applicable here - trying to run a railway that everyone can use is important - to call it "politically correct" suggests that it's just a politeness thing, rather than a legal requirement.
For a benchmark, look at how bus companies have scrapped marginal services, rather than continuing them with step entranced vehicles - maybe that inconveniences people but under the law that's how things have to be. Not saying it's something I wholly agree with or wholly disagree with but it's the law - got to deal with realities.
(and, to repeat myself, if TPE weren't able to replace 185s with old loco hauled stock before the 1 January 2020 deadline kicked in then there's probably no chance that TOCs will be able to replace accessible trains with inaccessible ones after the deadline - it's a nice idea - I like the nostalgic notion of keeping old trains running - but that's not the way that the law works)